A substrate plate for the manufacture of a mould for the production of optical registration carriers and a method for manufacturing same

Abstract: A substrate plate of plastic material instead of glass for the manufacture of a metal mould for the production of optical registration carriers of plastic material. Polyether imide is a suitable plastic material for forming the substrate plate. A suitable moulding process is injection moulding, wherein a highly polished mould is used.

Description: The invention relates to a substrate plate for use in the manufacture of a metal mould for the production of disc-shaped optical registration carriers of plastic material and to a method for manufacturing same. For the manufacture of a metal mould or father plate, also called mastering and electroforming, for the production of disc-shaped optical registration carriers of plastic material, such as CD's or LD's (video discs), use is made of glass substrate plates or master plates, see for instance EP-A-0 284 387 or US-A-5 096 563. The demands made of the surface of the glass substrate plate are very strict, so that finishing operations, such as grinding and/or polishing and brushing (with a view to removing a blue haze), are necessary. The contaminations produced in the grinding and/or polishing operations are difficult to remove. Furthermore demands are made of the eccentricity of the substrate plates. In this connection it is known to bond a metal plug centrally on the substrate plate or to make a central hole in the substrate plate or to use an accurate positioning unit, as in the applicant's AMS system. All in all glass substrate plates have the disadvantage of requiring laborious, time-consuming and cost-increasing operations. The object of the invention is to overcome these drawbacks and in order to accomplish that objective it provides a substrate plate of the kind mentioned in the introduction, which is characterized in that it is made of plastic material. The invention is further specified in the appended claims. The preamble of claim 1 is based on the above mentioned prior art. It is obvious thereby that the plastic substrate plate has a high surface accuracy, just like the glass plate, and is chemically and thermally inert with respect to the method for manufacturing metal moulds by using chemicals and heat treatment, and that the plastic material which is used for the substrate plates must be mouldable. Furthermore the surface accuracy of the substrate plate is determined by the moulding process and the moulding means used thereby, so that not every substrate plate needs to be worked individually, as is the case with the known glass substrate plates. Furthermore the substrate plate being proposed may be given a centring configuration in the moulding process, which configuration is determined by the moulding means, so that also in this case separate processing is not required. Furthermore the moulding process and the moulding means make it possible to vary the diameter and the thickness of the proposed substrate plate. Finally the plastic material of the substrate plate may be selected to absorb laser writing light and/or transmits laser measuring light from an order meter. In the latter case the proposed substrate plate must be of an optical quality. A suitable material is polyether imide, which is commercially available from GE Plastics under the registered tradename Ultem, in particular Ultem 1000 because of its reduced brittleness, a material which up to now has been used for products intended for use at elevated temperatures, such as microwave oven dishes, sterilization dishes and car light housings. The invention also provides a method for manufacturing the proposed substrate plate, wherein an injection moulding process is used. The mould thereby determines the surface accuracy of the substrate plate, so that said substrate plate is preferably highly polished, whilst the centring configuration may be determined by said mould. An operation that may be necessary when using the proposed method is to remove the static charge from the substrate plate following the injection moulding, which is not necessary when glass substrate plates are being used. The invention will be explained in more detail hereafter with reference to the drawings, in which: Figure 1 is a schematic sectional view of a substrate plate according to the invention; and Figure 2 shows the transmission curve of a polyether imide resin which is now preferred in combination with a photoresist mastering process. In the following description we will proceed as yet from a known photoresist method for manufacturing metal moulds for the production of disc-shaped registration carriers of plastic material, which is also known, and which may involve the manufacture of father plates and/or son plates or stamper plates. Figure 1 shows a schematic sectional view of an embodiment of the proposed plastic substrate plate indicated at 1. The upper side of the substrate plate 1 is indicated at 2, whilst the bottom side of the substrate plate 1 is indicated at 3. Reference numeral 4 indicates a central cylindrical projection to be used for centring purposes. In this case positive centring is concerned. It is also possible to use negative centring or a central hole, or no centring at all. In the last-mentioned case an accurate positioning mechanism must be provided, as in the applicant's AMS system. The use of the centring boss 4 is known to those skilled in the art for that matter. What is new is the fact that the centring boss 4 may be integrally formed with the substrate plate 1. In the aforesaid AMS system the diameter of the substrate plate 1 is thus some 16 cm, whilst the thickness is substantially 2 mm. It is obvious that the upper side 2 is the side which is coated with a photoresist when using the photoresist method. In order to obtain a satisfactory bonding of the photoresist a first coating may be applied to the substrate plate 1. The photoresist layer to be applied is also called the registration layer, because the desired information is registered therein by means of laser writing light. As already said before the substrate plate 1 is made of mouldable plastic material by means of a moulding process, in a centring configuration, if desired, inclusive of a projection 4 or a corresponding recess (not shown). Intrinsically to the purpose for which it is to be used, the plastic material used for forming the substrate plate 1 needs to be chemically and thermally inert with respect to the mastering process being used. In accordance with a possible and known photoresist mastering process a photoresist is applied to the upper side 2 of the substrate plate 1 at ambient temperature, whereby the solvents used are 90% methyl isobutyl ketone (MIBK) and 10% n-butyl acetate/xylene/2-ethoxy ethyl acetate. Then the substrate plate 1 with the applied photoresist are exposed to hot air, the conditions varying from 30 minutes at 80° to 6 minutes at 160° . Then the registration information pattern is written into the heat-treated photoresist in a laser beam recorder at ambient temperature, whereby no chemicals are used. Subsequently the photoresist layer is developed into a patterned photoresist layer in an NaOH solution. A metal film is applied to the developed photoresist by means of a vapour deposition process, sputtering or a wet chemical process. Subsequently a metal film is deposited at a pH of about 4 and a temperature of 50 - 60 °C in 90 minutes, using a solvent and chemicals, which metal film will be the metal mould after being removed from the substrate plate and being cleaned in order to remove any residual photoresist. Instead of the photoresist mastering process it is also possible to use ablative mastering processes, which are based on the evaporation of nitrocellulose. In that case a colorant is added to the nitrocellulose, which absorbs the laser writing light and heats the nitrocellulose, whereby the colorant and the wave length of the laser writing light are attuned to each other. With a suitable selection of the solvent it is possible to use for example polycarbonate or styrene malein anhydride as the substrate plate material in this mastering process. This is in contrast to the photoresist mastering process, since that process uses the solvent MIBK, as a result of which the aforesaid materials become diffuse and exhibit surface cracks, which phenomena do not occur when polyether imide resin is used as the substrate plate material. This latter material allows more freedom in the selection of heat treatment temperatures, also with the ablative process, because the transition temperature of glass is much higher than that of for example polycarbonate. The heat treatment may thereby be carried out in two steps of up to 130 °C each for 60 minutes. Another one of the several mastering processes that may be used is a mastering process whereby bulges are formed on the registration surface of the substrate plate. Returning to the photoresist mastering process it is noted that the substrate plate 1 must absorb the laser writing light in the laser beam recorder in which the substrate plate 1 is rotatably and centrally mounted, in order to prevent that false light be generated at the bottom side 3 upon exposure of the upper side 2 to modulated laser writing light. Thus the polyether imide resin absorbs the blue laser writing light used in the AMS system (see Figure 2). During the developing process it is furthermore measured whether the process has progressed far enough, by measuring the intensity of the laser measuring light emitted by the order meter and deflected by the indentations formed in the substrate plate. Thus polyether imide resin transmits the red laser measuring light of the order meter used in the AMS system (see Figure 2). With conventional photoresist mastering processes use is made of substrate plates of float glass (soda lime) having diameters of 240 mm and 360 mm and a thickness of 6 mm, which are obtained by grinding, polishing and washing, after which a metal centring boss may be provided. From the above it will be obvious, that when the substrate plates of float glass are replaced by substrate plates of polyether imide resin, it will be possible to use the same photoresist mastering processes and equipment that are being used for the glass plates. Figure 2 shows the transmission curve for Ultem 1000 (tradename of GE Plastics), whereby the transmission factor, in per cent, is set out along the ordinate and the wavelength, in nm, is set out along the abscissa. As said before the plastic material from which the proposed substrate plate 1 may be made, needs to be mouldable. The dimensions and the configuration, as well as the surface roughness of the coating side 2 of the substrate plate 1 can be determined by moulding the plastic material, whereby the term configuration refers to whether or not a positive or negative centring is provided; see projection 4. It should be borne in mind that in order to ensure the aforesaid quality the surface roughness of the bottom side 3 of the substrate plate 1 needs to be low as well. This can also be realized with a selected moulding process. Injection moulding is a moulding process which lends itself well for the present purposes. The mould used in the injection moulding process must be highly polished in that case, in order to obtain the desired low surface roughness for the upper side 2 of the substrate plate 1. It is preferred to remove the static charge from the substrate plate 1 subsequent to the injection moulding process, for example by means of an ionized air flow.

Claims: A substrate plate for use as a master disc in the manufacture of a metal mould for the production of disc-shaped optical registration carriers of plastic material, characterised in that said substrate plate for said master disc is made of plastic material. A substrate plate according to claim 1, characterized in that it absorbs laser writing light in a laser beam recorder. A substrate plate according to claim 1 or 2, characterized in that it transmits laser measuring light emitted by an order meter. A substrate plate according to claim 3, characterized in that it is of an optical quality. A substrate plate according to any one of the preceding claims, characterized in that the plastic material of said substrate plate is polyether imide. A substrate plate according to any one of the preceding claims, characterized in that it has a centring configuration. A method for manufacturing a substrate plate according to any one of the preceding claims, wherein an injection moulding process is used. A method according to claim 7, characterized in that the mould used in the injection moulding process is highly polished. A method according to claim 7 or 8, characterized in that following said injection moulding static charge is removed from the substrate plate. The use of a substrate plate according to any one of the claims 1 - 6 or obtained by means of a method according to any one of the claims 7 - 9, for manufacturing a metal mould for the production of disc-shaped optical registration carriers of plastic material.

Inventors: BISTERVELS FRANCISCUS MARTINUS, VAN HAM JOHANNA HENRICA MARIA, BISTERVELS, FRANCISCUS MARTINUS CATHARINUS MARIE, VAN HAM, JOHANNA HENRICA MARIA
Applicants: OD & ME BV, ODME INTERNATIONAL B.V.
Application year: 1994
Main classification: G11B7
IPC codes: B29D17, B29D11, B29K79, G11B7